This blog is dedicated to bringing World War II era documents to the general public, with an overall focus on armoured warfare.
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Saturday, 30 November 2013

On June 28th, 1919, Germany and the Entente signed the Treaty of Versailles, ending WWI, the largest conflict in the history of humanity at that point. A portion of German territory was annexed by the victorious nations, its colonies were also appropriated, it was forced to pay reparations. There were also harsh limits on Germany's military force. The land army was limited to 100 000 men, drafts were not allowed, a portion of Germany's warships were handed over to the victors, and the tonnage of new ones was strictly limited. Armoured vehicles (aside from outdated police cars) and aviation were forbidden. The conditions were such that their goal was, apparently, not to maintain peace in Europe, but to humiliate Germany and force them to take revenge.

Years before the nazis, Germany already started to, step by step, violate the conditions of the treaty. Aside from theoretical developments, which were not forbidden, the manufacturing base of the country slowly but surely accumulated experience. In 1925, a tank codenamed Großtraktor (large tractor) was developed. Leichttraktor (small tractor) followed in May of 1928.

The first mass produced German tank was the PzKpfw I. Work on this tank started in 1931, when the Directorate of German land forces drafted the requirements for a teaching tank, 5 tons in mass. The vehicle was officially named Landwirtschaftlicher Schlepper (agricultural tractor), which was not unusual in Germany at the time. Friedrich Krupp AG, Rheinmetall-Borsig, MAN, and Daimler-Benz AG received orders for this new tank.

Each company produced a prototype with more or less the same characteristics. The military liked Krupp's LKA tank the most. The best thing about it was not its technical characteristics, but that it was the project that could be built the fastest, and the cheapest. Five of Krupp's tanks, still without armament, were tested at Kummersdorf in the summer of 1933. The tests demonstrated insufficient reliability of the transmission and suspension, forcing Krupp's engineers to make some changes. After that, 15 more vehicles were given the green light. The vehicles were assembled at multiple factories. This unorthodox decision was made to distribute the tank building experience.

The hull and turret were developed by Daimler-Benz. A welded hull protected the crew and components from bullets. The turret, also welded, was placed to the right of the tank's axis. The maximum armour thickness was 13 mm. The tank was equipped with a Krupp 57 hp engine, theoretically making it capable of accelerating to 37 kph. The tank's armament consisted of two 7.92 mm MG-13 machine guns.

The first mass produced chassis were made in December of 1933. In July of 1934, the tank started mass production. In the same year, the first tanks started arriving at training centers. By October 1935, Germany's first tank divisions were formed. That is when the tank received its name: PzKpfw I. According to foreign historians, there were about 1100 vehicles of the first configuration built.

When the tank entered the army, its downsides quickly showed themselves. Its engine was too weak. Instead of the ideal 37 kph, it could only reach 28 kph. Work started on an improved PzKpfw I Ausf. B. Retroactively, all existing tanks were named PzKpfw Ausf. A.

In 1935, the new six cylinder water cooled Maybach NL 38 TR engine was chosen for the tank. The new engine was more powerful, at 100 hp. Because it was larger than the engine compartment of the PzKpfw I, the tank became longer by 40 cm. The tank gained another road wheel, and an idler was lifted to make turning easier.

Interestingly enough, no work on improving armament was conducted. First "B" tanks were equipped with the same MG-13s, and later, dual MG-34s. These machine guns fired a little faster, but had the same rifle caliber. If the firepower was improved, it was so miserly, that it is not worth mentioning.

The PzKpfw I Ausf. A remained in production until 1937, and the chassis until 1941. The PzKpfw I was seen as a strictly training tank. However, as it often happens, reality interfered. Until 1937, the PzKpfw I was the main tank of the German army. Germany started WWII with over 1000 PzKpfw I of both modifications.

The tank saw its first combat in Spain, during the Spanish Civil War. Various sources record 32-41 tanks shipped along with the German volunteers of the Condor legion, fighting on the side of Franco. These tanks formed the Drohne tank group. Despite the fact that the group's main function was to teach Spanish tankers, the group frequently saw combat. The very first battles showed the superiority of Soviet T-26 tanks, armed with cannons. Armour piercing bullets could penetrate the T-26 at 120-150 meters, but it was hard to close in to that distance, as the T-26's 45 mm gun could destroy the PzKpfw I at any range.

In order to somehow improve the situation, there was an attempt to install the Breda 20 mm autocannon. In order to fit the gun into the turret, it had to be modified with a cylindrical addition. There is no data on the combat use of this "homebrewed" vehicle.

In 1938, Germany started expanding its territory. PzKpfw I took part in the Anschluss of Austria. Here is where the PzKpfw I showed its poor reliability. At least 35% of both types of tank broke down and were abandoned by the side of the road during the march. In order to conserve the negligible number of tanks, they were delivered to the Sudetenland by trucks.

During the Polish campaign in 1939, most tanks in the German army were still PzKpfw Is. Weak armour and armament were apparent. 320 tanks were lost, but most were repaired by the Germans.

At the time of Germany's advance in the West, only 550 PzKpfw I tanks remained, and they were assigned secondary roles. Even then, the losses were very great, and 182 units were lost irreparably.

As time went on, the amount of PzKpfw I tanks declined. In the West, as well as the East, they were used until 1944, primarily to combat partisans.

Small amounts of PzKpfw Is were shipped to China, Hungary, Spain, and, according to some sources, Croatia.

Friday, 29 November 2013

WWII era artillery shells are all look more or less the same to the untrained eye. However, much ink was spilled in the discovery of what shape was best. Documents in CAMD RF 81-12042-85 tell a small part of that story. The document is almost entirely text, so I will not include scans. They can be found here.

"In all nations, without exception, armour piercing shells for anti-tank and field artillery are produced with sharp tips. Our shells (45 mm and 76 mm) are made only with blunt tips. Comparing their effect on tank armour shows an advantage of sharp armour piercing shells over blunt armour piercing shells.

Blunt tipped shells migrated to land artillery from naval artillery, because a blunt shell penetrates heterogeneous (for example, cemented) armour, hardened on the surface and softer in the back. This armour is commonly used on battleships.

Homogeneous armour, armour with uniform hardness, resists blunt shells much better than sharp shells. On tanks of all countries, including Germany, armour is homogeneous, which means that using sharp tipped shells will be more effective than blunt tipped shells. Sharp tipped shells also have an advantage when fired at an angle, which happens most often. A blunt nosed shell that hits armour at an angle ricochets. A sharp nosed shell, when hitting the armour, bites into it, and penetrates. The comparative effects of sharp and blunt 45 mm armour piercing shells are shown on the table below."

The performance of the sharp tipped shell is the upper row. The performance of the blunt tipped shell is the bottom row. The table shows distances at which the shells penetrate, in meters, at the specified angle. The blunt nosed shell performs more poorly against 40 mm of homogeneous armour every time, and does not penetrate at all when the armour is sloped 45 degrees.

There are two reasons why we do not need to worry about the armour piercing properties of our shells. One is that our 45 and 76 mm guns are very powerful. The other is that German tanks are weakly armoured (40-50 mm in the front, 30 mm on the sides), and German armour is of poor quality.

These two factors somewhat mitigate the deficiency of blunt nosed shells.

Experience shows that the Germans keep increasing the thickness of their armour (in part, the front section of all German tanks has additional screens), and the mass of German heavy (PzIV) and medium (PzIII) tanks keeps growing. We must be ready to penetrate thicker armoured German tanks. This can be accomplished by means of using sharp-tipped shells. The penetration of sharp tipped shells may also be increased by using any of well known methods (variable hardening, cementing, welding on a ballistic cap, etc).

I think that it is imperative to immediately begin production of sharp-tipped armour piercing shells for anti-tank artillery.

June 27th, 1942

V. Malyshev"

Malyshev was right, German tanks kept getting more and more armour. However, GAU KA responded to his letter a few days later:

"The influence of tip shape on penetration was studied at GAU KA as soon as armour piercing shells were introduced to land artillery.

In 1935-36, ANIOP, under orders from the GAU KA, performed a study on this topic (NIR #25, 1936), which led to the following conclusions:

"All armour piercing shells must be produced with a blunted part about 0.7 calibers long, as shells with this blunting need less speed to penetrate an armour plate than shells with a sharp tip under most conditions." (part 8 in NIR-25, 1936).

Further along, as armour quality improved, and as necessity to produce improved armour piercing shells increased, trial shells frequently were developed in two variants: sharp tipped and blunt tipped, and were tested on homogeneous and heterogeneous armour plates.

During the last pre-war years (1939-1941), development and testing of improved armour piercing shells was performed with cemented armour, over 30 mm thick, with resistance coefficient K=2500-2700. The reason for this was that the Izhor factory sent GAU KA the sturdiest armour plates, the cemented ones. Additionally, the so called "destructiveness" of the tip of the shell was higher for cemented plates than homogeneous ones. As such, tests against cemented armour were considered more rigorous when it came to examining shell quality. New types of shells were usually also tested against homogeneous armour.

We did not have precise information on armour plates of our enemies, so GAU KA had to make sure its engineers produced shells that are effective against both homogeneous and cemented armour, as ordering shells that work only against cemented or only against homogeneous armour would have been incorrect.

The main characteristics of a shell hull are the following: speed of penetration, hull sturdiness, and lack of ricochet.

NII-48 trials (see report #1757ss dated November 19th, 1940), ANIOP trials (see report #0264ss-40), and trials of the Main NKSP Directorate demonstrated that sharp tipped shells work better against homogeneous armour at 0 degrees, and require less speed than blunt tipped shells, but work worse against cemented armour.

When shooting at a plate at an angle away from normal, as the angle increases, performance of the sharp tipped shell decreases compared to the blunt tipped shell, against both cemented and homogeneous plates.

The blunt nosed shell can survive an impact against armour better. Usually, the sharp tipped shell penetrates the armour 30-40 mm away from the place of impact at a 30-45 degree angle, which means the chance of ricochet is higher.

The rigidity of the sharp shell is worse when shooting at an angle, compared to a blunt shell.

The above examples of theoretical and experimental works fully back the decision to adopt blunt-tipped shells. Study of captured armour piercing shells and their comparative trials showed that:

All captured shells without ballistic caps are sharp tipped. If there is a ballistic cap, the tip is dulled.

The front part of the shell is very hard (up to 62-65 Rc), which is achieved by:

use of instrumental steels

welded on tip

very fine grinding, and even polishing, of the shell tip

Domestic armour piercing shells are made from more ductile 35 HGS grade steel, and, according to work of NII-24, are not improved by the above methods.

Sharp tipped armour piercing shells are only superior when manufactured from instrumental steel. At this time, the transition to instrumental steel, requiring special thermal treatment for the required high hardness and polishing of the shell tip or a welded on shell tip, would be difficult, and production of large amounts of these shells is not possible.

In order to evaluate the penetration of sharp-tipped armour piercing shells made from instrumental steel using our calibers, GAU KA gave an order to produce these shells at the beginning of 1941, but they were still not manufactured."

Thursday, 28 November 2013

In 1940, two tanks were ordered to replace the KV-1: the T-150 (also known as Object 150, KV-3, and 150) and T-220 (also known as KV-220, Object 220, or just 220). The tanks were much heavier than the KV-1, and thus required much more powerful engines.

CAMD RF 38-11355-6

"Minutes of the joint commission for the trials of 700 hp and 850 hp engines, produced by factory #75, and field trials of T-150 and T-220 tanks, produced by the Kirov factory, in which these engines are placed.

Present:

Chief engineer of factory #75, comrade T.P. Chupahin

Chief of the Kirov factory tank department, comrade A.I. Lantzberg

From BTU KA

Military engineer first class, comrade Gluhov

Military engineer third class, comrade Kaulin

Military engineer third class, comrade Voroshilov

The commission decided that:

The engines were accepted for field trials too soon.

The engines need factory trials, not field trials.

In order to swiftly complete the engine corrections, transfer the tanks to the intra-factory commission for factory engine trials.

The commission for engine trials should include the BTU engineer in charge of the T-150 and T-220.

Finish the trials before March 10th. The Kirov factory and factory #75 must provide normal conditions for the engines inside the tanks and provide tanks with working engines and cooling systems for field trials by this date."

Looks like they got too hasty. The 850 hp engine didn't get anywhere, but the KV-220 ended up with a V-5 engine turbocharged to 700 hp by April.

CAMD RF 38-11355-6

"To the chief of the 3rd department of the BTU KA, Military Engineer 1st class, comrade Afonin

In addition to the report from April 20th, 1941, I report the following with respect to completed trials:

By May 4th, 1941, object #220, with additional weight to simulate the weight of a KV-3, endured 967 km worth of trials. Of those, 448 were on a road, and 519 were off-road. The V-5 engine worked for 68 hours and 30 minutes.

During trials, the following failed:

Balancer with idler axle: 6

Lower road wheels: 2.5

Torsion bars: 1

Idlers: 2

In addition to the note from April 20th, the following defects were discovered:

The 2nd and 4th gear pins in the gearbox were sheared off.

The eyelet of the main friction clutch was destroyed.

No defects were found in other components of the transmission during technical inspection.

It is necessary to point out that the off-road conditions were especially difficult, and the V-5 700 hp engine only reached second gear. Third gear is only usable on the road or hard ground.

During trials, the following data was obtained:

Highway fuel efficiency: 2.9-3.2 liters per kilometer"

Sadly, this is the only page of this document that I have, but I think it gets the idea across. Keep in mind that the already portly 62 ton tank was loaded to 70 tons, heavier than any other Soviet tank that was built.

Wednesday, 27 November 2013

The idea that Soviet tank designers gave no thought to ergonomics is very common in Western media, but it is simply not true. Soviet designers were taught to take ergonomics into account, as illustrated in a chapter of Engineer-Colonel Samusenko's book Foundations of Design of Armament for Self Propelled Guns and Tanks. I'm not going to translate the entire chapter, but it contains some useful data.

"In order to avoid [crewmen] hitting the roof when traversing bumpy terrain, the height of the roof must be 900-980 mm above the seat. The upper limit is for a gunner of above average height (175 cm) in a sitting position (fig. 10).

Figure 10. A gunner sitting.

Since the loader's position changes based on remaining ammunition locations, his body moves during his work, and the indicated numbers do not provide him with a comfortable work environment. A loader requires at least 1450-1500 mm (halfway between standing and sitting), or 1750-1800 mm for only standing (fig. 11). The absolute minimum height of the fighting compartment is only acceptable when the loader has shells delivered to him from the ammunition rack by an automatic mechanism, and can remain sitting.

Figure 11. The size of an average person.

Figure 12 shows the comfortable position of a driver in low spaces.

Figure 12. A driver in cramped conditions.

With a low breech axis, when the breech is lower than the loader's elbow, a vertical breech is more convenient. With a high breech axis (950-1000 mm or more), a horizontal breech is more convenient, pointed towards the loader's side.

The fighting compartment must connect with the driver's compartment for communication and interchangeability of crew members. The hatches should be positioned comfortably, and be 500-600 mm in width."

The textbook also contains some crew space numbers, for reference.

The table lists the tanks in this order: MkIV (Churchill), Cromwell, T-34 (numbers indicate that this is the T-34-85), IS-2, PzIII, PzIV, M4A2 Sherman, Panther, Tiger.

The first column is the sequential number, the second is the tank's name. The third is the tank's mass in tons. The fourth is the location of the transmission: the first 4 tanks have it in the rear, the rest in the front. The fifth is the caliber of the gun on the tank. The sixth is the number of crewmen in the turret. The seventh is the diameter of the turret ring in millimeters. The eight is the width of the gunner's space. The ninth is the size of the loader's space. The tenth is the height of the fighting compartment, from floor to turret ceiling. The eleventh is the size of the fighting compartment, in meters cubed. The twelfth and thirteenth are the same for hull and turret respectively. The last is volume occupied by crew and components.

The table after contains similar data for some SPGs: the SU-100 and ISU-152.

The first column is the name of the SPG, the second is the total fighting compartment volume, then the space occupied by ammunition, crew, and equipment. The fourth column contains the number of crewmen. The fifth contains the volume necessary for the crew to move around. The last column is the "comfort coefficient", the total volume divided by consumed volume. The textbook warns that a high comfort coefficient provides the crew with comfortable working conditions, but a coefficient that is too high is indicative of an inefficient design.

Let's compare the numbers of these vehicles. Despite the accusations of uncomfortable Soviet tanks, the Churchill's crew is the one with the least space. The gunner only has 460 mm of space, a centimeter more than the average shoulder span of a Soviet tank crewman. Harsh. Everyone else enjoys approximately the same amount of space, with the Panther going slightly above the mean. Certain posters from the World of Tanks forums will be delighted to learn that the Sherman was, indeed, the most comfortable tank in this list for the gunner.

The loader's position varies a little more. The Churchill's loader is ridiculously constricted, and the Cromwell's isn't doing much better. The T-34-85's loader has almost as much space to work in as the PzIII's loader, and lives a life of luxury compared to the PzIV's loader. The PzIII and Sherman are tied for the most room for the loader among the medium tanks. The IS-2 and Tiger, as the largest tanks on the list, have the most room for their loaders.

The height of the fighting compartment is where the Churchill shines: that is the only tank where the statistically average Soviet crewman can stand to full height, followed shortly by the PzIII and the Cromwell. In the rest of the tanks, he must sit. The PzIV has a pretty abysmal fighting compartment height, even less than the Soviet requirement for a half-standing loader, which bodes ill for the crew's comfort. Sadly, the space used for crew movement is not given in this table, making calculation of a comfort coefficient impossible.

In conclusion, this book teaches us two things. One is that Soviet engineers cared about ergonomics too. The second is that British people are apparently very tall and disproportionately narrow.

Tuesday, 26 November 2013

The North-Western Military Production department sent a note the Bolshevik factory, which consists of the following: "This is a notice of a GUVP announcement that a request for a support tank was made on July 25th, 1925 for #-V-534s

Description of the request

Build one regimental support tank with machine guns and a 37 mm cannon, which will be delivered to the factory by GUVP. The estimated price is 25000 rubles, with 2500 rubles for the immediate development of an engine.

Due date: August 1st, 1926

Reasoning: memorandum #6247 from the Technical Bureau, secret, from July 13th, 1925. Note: blueprints and technical details are developed by the Technical Bureau of the GUVP and the design bureau of the Bolshevik factory.

The due date is 12 months from now. Funding has already been transferred. Blueprints and data necessary for development of the engine are already present at the factory.

Blueprints of the suspension will be provided by the Technical Bureau in August-September. Armour layout blueprints will be ready by October-November of 1925. The Technical Bureau states in advance that the armour will be 16 mm thick for vertical plates and 8 mm thick for horizontal plates, and proposes that the metallurgist of the factory, engineer Rozhkov, explores the topic of lowering the required thickness of armour over the next two months, and provides final results and prototypes.

The requirements are resistance to armour piercing three line bullets [Note: a line is one tenth of an inch, so .30 cal or 7.62 mm] at 25-50 paces. Thinner armour is a desirable accomplishment, but not a requirement, as calculations allow for armour up to 16 mm thick, and 16 mm thick armour should meet the requirements.

There are no requirements for chemical and mechanical properties of the armour of the first experimental prototype. Attachment: mass of the armour plates:

15 tanks are to be assembled each month, with the condition that the Izhor factory supplies the riveted armoured hull, turret, and turret ring. Additional expenditures must be made to convert the former artillery shell workshop.

131 additional pieces of machinery are required for the production of 150 tanks annually. Lateness of blueprints will delay the rest of the project.

August 21st, 1925.

Blueprint #1623, the overall view of the support tank controls, is sent. This is enough to develop the engine and the tank's overall layout. Almost all suspension blueprints have been completed and copied by the Technical Bureau. The transfer of the blueprints is delayed due to some changes that became necessary during development. The blueprints will be transferred to the factory by September 7th, 1925.

September 2nd, 1925.

The first group of the working suspension blueprints mentioned in request #V-534s has been sent. A memo is attached with an outline of the blueprints and a table of steel grades which the Technical Bureau assumed in their calculations. Additional blueprints of the support tank have been sent: overall view and dimensional view with several altered values. Destroy the blueprints with unaltered values currently in your possession."

The document is a transcription, not an original. It seems that a mistake was made when copying over armour figures; the density of the plates is not only different for the two thicknesses, but both are impossibly low.

Sunday, 24 November 2013

The Germans were very well known for using obsolete tank chassis to create tank destroyers. The Marder series, the PzJg I, and several other designs gave new lives to obsolete light tanks. The Soviets also considered such a move.

"Report of Military Engineer 1st class comrade Afonin on a potential plan for constructing SPGs.

Install a 25 mm automatic AA gun on the ZiS-32 and ZiS-36 vehicles, as well as the T-40 tank and STZ-5 tractor (with lengthened base and ZiS-16 engine).

Proposals:

A 57 mm ZiS-4 gun cannot be used on the BT-5, T-26 and STZ-5 as a tank destroyer for the following reasons:

Weak armour.

Overloading the suspension (T-26 and STZ-5).

Low operational range.

Low ammunition capacity.

It is agreed that an SPG made using STZ-5 components and armed with a ZiS-4 57 mm tank gun could be used as a self propelled anti-tank weapon.

An SPG made using T-40 components with a 57 mm anti-tank gun is feasible.

The 85 mm AA gun cannot be installed on the Voroshilovets tractor for the following reasons:

Weak suspension (when armour is added).

Bore axis is too high."

Well, most of these didn't pan out. However, after subtracting the second list from the first, the following vehicles are deemed feasible:

T-50 with a 57 mm gun.

A-42 tractor with an 85 mm gun.

T-26 with a 76.2 mm gun.

25 mm or 37 mm AA autocannons on the T-50, T-26, BT, T-40, and STZ-5, as well as some trucks.

The document is dated June 9th, 1941, so I assume that a lot of these were forgotten when the Germans showed up. However, if you're into alternate history or bashing some model kits together, that should give you plenty of new ideas.

The Soviets never quite got around to making any of those T-26 based tank destroyers, but someone did. Pz.Jag.Abt. 563 converted 10 T-26es into tank destroyers in 1943. In March of 1944, they were replaced with Marders.

As you can see by looking at the gun shields, each vehicle is slightly different. This was clearly a field conversion done out of necessity rather than something done at a factory with actual schematics.

In November of 1941, a plan came out for next year's experimental SPGs. Among the many vehicles is a directive to mount a 76 mm USV or ZiS-3 gun on the T-60. The T-60 couldn't quite manage the extra load, but, next year, a solution came: the T-70. The T-70 was sturdier, and gave the ability to finally mount the ZiS-3 gun.

"Experimental prototype of the SU-76 (SU-12) SPG built by factory #38"

CAMD RF 38-11369-1

"In accordance with the decision of GOKO, factory #38 designed and produced an experimental SU-12 SPG, in October-December of 1942. The SU-12 SPG consisted of a 76 mm ZiS-3 gun on a special chassis composed of T-60 and T-70 elements. The engine assembly and transmission were positioned in parallel. The prototype was tested at Gorohovets during December 6th-16th and December 29th-31st, 1942.

The SU-12 SPG passed trials, and was recommended by the GAU KA for the Red Army.

GOKO decree #3530 from June 7th, 1943 removed this SPG from production. The 560 SPGs that were built were modernized."

...

"According to GOKO decree #3530 from June 7th, 1943, experimental prototypes of the SU-15 and SU-16 were trialled at Gorohovets in June of 1943 by a commission led by Major-General comrade Pechenikin of the tank engineering service. It is worth noting that the GBTU KA and the commission checked the transmission and motor assembly especially thoroughly, as it performed unsatisfactorily on the SU-76 (SU-12)."

"Experimental prototype of the SU-76M (SU-15) SPG built by factory #38"

CAMD RF 38-11369-1

"Experimental prototype of the SU-16 (SU-38) SPG built by factory #38"

CAMD RF 38-11369-1

The "hard characteristics" of the two SPGs were more or less equal. The SU-76M had a small advantage over its five-wheeled brother: its average off-road speed was 0.5 kph higher and it had 5 degrees more gun elevation. However, comparing tanks is not that easy.

"It was discovered that the SU-15 SPG is more stable than the SU-16 during movement, and has a larger fighting compartment."

Several defects were discovered in both SPGs, but the SU-76M performed so impressively that it was accepted into production before a second prototype was built. Trials in August of 1943 confirmed that the choice was correct.

"The SU-76M SPG did not undergo significant changes until today. In 1944, a partial modernization and industry experience raised the quality of the SU-76M to the point where these SPGs can pass trials 3000 km long.

Engineer-Major comrade Lisin's contribution to the trials and improvements cannot be glossed over. Thanks to his determination, a series of defects was resolved in experimental prototypes and pre-production run.

Factory #38 took four months to get the SU-76M to mass production quality, which is a good figure, especially considering the difference between it and the SU-76 (SU-12).

The SU-16 SPG was deemed inferior to the SU-15 (SU-76M). Work on this SPG ceased when the SU-76M entered mass production."

The 1944 modernization also equipped the vehicle with a DT machinegun, and ports in the sides from which it could be fired. The MG could be mounted on the rear to fire at airborne targets.

Even though the SU-76M was already accepted for mass production, development of similar vehicles did not cease. The SU-NATI-TsKB SPG was developed in July-October of 1943, consisting of a custom built chassis using T-80 and BA-64 components and a 76 mm K-3 gun, with ballistics equivalent to the 76 mm S-54 AA gun.

"Experimental prototype of the SU-NATI-TsKB SPG"

CAMD RF 38-11369-1

The new SPG was very different from the SU-76. It had a fully closed fighting compartment in the front of the hull. The gun was much more powerful. Both gun depression and elevation were improved. It had the same mass as the SU-76, but had a weaker engine (2x54 hp), a lower top speed (35 kph), and worse horizontal gun traverse. The SPG had serious problems with ergonomics, and did not even make it to trials.

Molotov factory (GAZ) had their own horse in the light TD race. 3 horses, even: SU-74, SU-74B (SU-57B), and SU-74D. The SU-74 was similar to the SU-12: a rear gun placement (except with an F-34 instead of a ZiS-3), front ZiS-16 engine. However, the engine failed four times over 198 km of trials in 1943, and further trials were not performed. Work on the vehicle was discontinued. That same year, the factory attempted to design a light tank destroyer once more, with the SU-74B.

SU-74B, despite its similar index, was a radically different design. The fighting compartment was now in the front instead of the back. The engine and transmission were placed in the rear. The engine was the same ZiS-16, turbocharged to 104 hp. However, this engine power was not sufficient, and the TD failed trials in August-September.

"Experimental prototype of the SU-76B SPG, designed by the Molotov Automotive Factory "

CAMD RF 38-11369-1

Much like the SU-76, the TD weighed 10.5 tons and had a crew of 4, with 25 mm of armour in the front and 15 on the sides. The weak engine could only provide a maximum speed of 28.8 kph. The ZiS-4 57 mm gun could traverse vertically between -5 and +14.33 degrees and horizontally in an 18 degree arc.

A third attempt in that same year was the SU-76D. It used the same hull, and an American made GMC diesel engine, with a different transmission. The vehicle's drive wheels were in the front. The gun was once again a 76 mm F-34. It ended up being heavier than the SU-76B, at 11.8 tons. In the same August-September trials, the vehicle was deemed acceptable, under the conditions that the engine be replaced with an improved domestic ZiS-16 and mass reduced to 11 tons. However, due to the adoption of the SU-76M, and the fact that Molotov factory could not make the required improvements in time, the SU-76D was not adopted by the Red Army, and work on it ended. The document points out that Astrov's three TDs were perfectly fine designs, but the ZiS-16 car engine could not cope with running at maximum load for a long time.

"Experimental prototype of the SU-76B SPG, designed by the Molotov Automotive Factory "

CAMD RF 38-11369-1

The 110 hp diesel engine allowed the TD to reach a maximum speed of 35.8 kph, even though the average speed was not much higher than that of the SU-76B (26.6 kph vs 27 kph). The gun range was similar: -5 degrees depression, 14 degrees elevation. Despite the larger weight, the SPG carried the same amount of armour.

In September of 1943, after the adoption of the SU-76M, Molotov factory redirected their efforts to modifications of that TD. Their first modification was quite impressive: the gun was replaced with a more powerful D-5S, and the front armour increased to a whopping 82 mm. The fighting compartment was now entirely closed. The TD was named "SU-85", with no way to differentiate it from the SU-85 on the T-34 chassis.

"Experimental prototype of the SU-85 SPG, designed by the Molotov Automotive Factory "

CAMD RF 38-11369-1

With the same pair of 70 hp engines, the 14 ton TD could reach a top speed of 36.3 kph. The TD passed 1045 km and 152 rounds of trials, but was not recommended for production, as 10 hp/ton was deemed insufficient.

In May-September of 1944, Astrov made yet another 85 mm TD: the SU-85A. This vehicle was much closer to the mass produced SU-76M, with an 85 mm gun, a TSh-15 sight, and with additional springs on the road wheels. The SU-85A was tested much more thoroughly: 1570 km and 824 rounds at Gorohovets proving grounds, then 1028 km and 234 rounds at the NIBT proving grounds in January of 1945. The verdict was that the SU-85A requires further modification to achieve higher stability after firing and more engine power to improve off-road performance.

"Experimental prototype of the SU-85A SPG, designed by the Molotov Automotive Factory "

CAMD RF 38-11369-1

The mass of the SU-85A was reduced to 12.3 tons. That, with the same two engines, allowed it to reach a speed of 39.8 kph. This time, the front armour was the same as the SU-76M, only 25 mm.

The SU-85A's successor, the SU-85B, was ready for trials in April of 1945. The vehicle was trialled for 1000 km and 800 rounds, and passed the trials. The more powerful engines and LB-2 85 mm gun with a muzzle brake solved previously encountered problems. Crew placement in the new widened fighting compartment allowed a very high rate or fire with the 85 mm gun, up to 10 RPM.

"Experimental prototype of the SU-85B SPG, designed by the Molotov Automotive Factory "

CAMD RF 38-11369-1

The vehicle now had a GAZ-203 model 15V engine, with 160 total hp, allowing it to nearly match the top speed of the SU-76M (43.5 kph vs 45 kph), despite its 12.4 ton mass. Unfortunately, problems arose when mass producing the LB-2 gun, leading to delays past the end of the war.

The SU-76M was also modified with 57 mm guns at the Molotov factory. Two prototypes were built, one with the same fighting compartment, and one with an altered fighting compartment, and an armoured roof. After 270 rounds fired from the first prototype and 358 rounds from the second in trials during May-June of 1944, the second prototype was recommended for adoption by the Red Army.

"Experimental prototype of the SU-57 SPG, second variant, designed by the Molotov Automotive Factory "

CAMD RF 38-11369-1

The vehicle was armed with the longer ZiS-2 57 mm gun, growing in mass by 200 kg, but otherwise unchanged. However, since the primary purpose of the SU-76M was infantry support, GBTU was unsatisfied with reducing the caliber of the gun, as well as reduced accuracy when firing at moving targets and poor ventilation of the fighting compartment. Installation of a roof and a gun with higher armour penetration was deemed undesirable.

Work on light SPGs did not end here. The SU-76M proved itself to be a powerful ally of infantry. Lightened versions of the vehicle were developed for airborne operations, but I will leave that for another article.

The following document contains Guderian's thoughts on positioning tanks and anti-tank guns in combat. His unique writing style is preserved.

"Translated from German
January 17th, 1945

Instruction on combat action #37 (Combat of tanks and ATGs)

The following material, borrowed from combat experience, contains valuable theoretical and practical instructions, which will aid not only tank commanders and gunners, but also tank destroyers, AT gunners, and soldiers of all forces that combat tanks.

The main observation source of a tank is the commander. What he observes is told to the driver. The turret gunner can only observe through the scope. Because of this, his view range is limited to 24 degrees, and is blurry on the edges, or, in conditions of poor visibility, completely blurry. The commander will tell him the initial direction of fire, and other data.

Aside from the commander's primary task of fire correction, the commander must point out the road to the driver, keep track of the direction of attack, and maintain formation. His view range is also limited (unless he can stick his head of of the hatch), due to looking through thick glass or side refractors. Using the periscope is difficult due to shaking.

It is important to know that an inexperienced commander tends to observe the area in front of a tank, limiting his field of vision to about 120 degrees, and does not pay attention to the sides, being busy with "current events". It is rare to see a tank with a periscope pointed in any direction but the direction of motion.

To put it simply: a tanker is grateful to a target that takes into consideration these difficulties and places itself where it is easy to spot, and get upset when it is not so cooperative.

Tanks like when the target is in the direction of movement, since the turret does not need turning, and it is easy to prepare initial data for the gunner.Tankers do not like when ATGs are positioned in such a place where you need to turn your head to spot them. While you are turning the turret, something unfortunate may happen.

Tanks like when the muzzle flash, which is usually the only sign of an anti-tank gun, can be seen in front of some bushes, structures, or some other background that is easily spotted. This makes aiming much easier.Tanks get angry when the muzzle flash is seen in the open, and good camouflage and positioning of the enemy gun does not give the commander any reference points, so he is forced to wait for a second shot. While the gunner turns his turret, it may be too late.

Tanks like when the muzzle flash is far away, as even if the shell strikes the thick front armour, it is not likely to penetrate, and the tank can calmly return fire.Tanks feel unease when the flash is close, and aiming must be done quickly. In this case, it is very likely that the next shot will hit the tank.

Tanks like when dug up dirt, moving people, and driving tractors indicate that something is up. Tanks can't stand when nothing is visible and everything pretends to be still and peaceful, or when fire comes from a different direction.

Tanks are happy to deal with a single ATG, and can calmly deal with it without interference from other guns. Tanks rage when they get caught in an ambush and must fight several ATGs at once.

Tanks are thankful when enemy ATG positions are so easy to spot that the artillery forward observer has enough time to call in and correct artillery fire.Tanks are lost when the observers cannot detect hidden and properly dispersed, lengthwise and width-wise, enemy AT guns, which makes it impossible for artillery to open fire on them.

Tanks are happy when, after taking fire, they can swiftly take cover in a depression and then attack the ATG position from another angle.Tanks are very disappointed when they get hit from another direction during a flanking maneuver.

Tanks value cases when a combination of a flank and a forward assault can take out a whole ATG position on one move. Tanks can't stand when they attack an ATG position, and are hit from a flank by another ATG, even if the latter fires at under 100 meters.

Tanks prefer to locate obstructions before an attack: bridges, etc, in the so called "tank-accessible terrain". These obstructions are easy to go around with a feint or by entering unfavourable terrain.Tanks get upset when they get baited by a weakly resisting front and are rewarded for their sweet advance with fire from both flanks ("Fire sack").

Tanks feel swell when they can combat enemy ATGs while sitting still in a comfortable spot. Tanks get sad when the stop at an elevated point for observation, and take a shot to their stomach from a short distance.

Tanks prefer defences that can't fire in all directions. Tanks are unhappy when an ATG position can fire in all directions, especially directions where the tanks were planning on moving.

Tanks are calm when ATGs fire from well prepared and camouflaged positions, but do not change them. Tanks are enraged when they take fire from ATGs from previously unoccupied pillboxes, houses, or positions.

Tanks prefer to have an enemy tank in front of them than an ATG on the flank.

Guderian.

Sent to HQ down to battalion level, including allied forces.

Translated by the translator of the 9th Guards Army HQ

Senior Sergeant Golant

Confirmed: Senior assistant of the chief of the Armoured and Motorized Forces of the 3rd Ukrainian Front

Saturday, 23 November 2013

What do you do when you have a ton of old tanks kicking around? If you're the Germans, you throw away the turret, and put a bigger gun on top. However, that approach means you still have half of an obsolete tank, with no spare parts for it. The Soviets had different ideas: bury them.

Not entirely, of course. Think about the parts of the tank that wear out the most: the engine, the tracks, the road wheels. A tank can be immobilized by broken parts, and waste a perfectly good gun in the process. If you have a bunch of broken or nearly broken tanks, might as well drop them off somewhere they can be useful. Also, dig them into the ground, since they're not going anywhere anyway.

The following photos show some more MS-1s. These are armed with 45 mm guns, and have their "tails" removed. They haven't been dug into the ground yet, but they are going to be.

Interestingly enough, not all MS-1s met their end in a ditch. This page lists 3 MS-1s as a part of the 150th Independent Tank Brigade as of February 26th, 1942.

Here's a rare one. That's not just any tank dug into the ground. That's a T-46 tank! They were meant to replace the T-26, but never quite managed to. A lot of them also ended up as fortifications as their final role.

Pre-war light tanks weren't the only ones to end up in the ground. A letter from the GAZ factory to GABTU from 1942 talks about 379 hulls for obsolete T-40 and T-60 tanks, and states that 150 hulls are available to GABTU to use as pillboxes.

Of course, not only light tanks became obsolete. Another letter to GABTU, this time from a tank school, states: "The school has 4 T-35 tanks and 8 T-28 tanks, which, after long use and numerous repairs, have become unusable and cannot be restored with the resources of the school. I await your instructions regarding transfer of these tanks to the armoured train directorate in order to install them as weapons platforms or immobile gun batteries in fortified regions." This letter was sent in 1943, long after those tanks would have been useful in combat. Let's see how this turned out:

CAMD RF 38-11355-963

Instead of leaving the turret on and using the tank's cannon, this pillbox design simply re-uses the hull.

Something similar was done with the KV-1S:

CAMD RF 38-11355-963

During the defense of Leningrad, everything that could shoot was used, including the experimental Kirov T-50 tank. A curio of the Winter War, the T-100-Z, contributed to the defense, but not in its entirety.

"Leningrad Front. A tank that became a pillbox. Photograph by special correspondent A. Kapustyanskiy."

The Soviets were far from the only ones to bury their old tanks. Here is a British Medium Mk III buried at Mersa Matruh.

Friday, 22 November 2013

During the Battle of Kursk in the fall of 1943, it was discovered that the 122 mm A-19 gun could effectively penetrate the German Tiger tank at any distance. Joseph Kotin, famous Soviet engineer, proposed the installation of this gun in the heavy IS tank, instead of the 85 mm D-5T.

The only possible way to do this in a short amount of time was to install a muzzle brake. This device allowed to place the gun on a universal mount without significant engineering effort. The military did not like the muzzle brake idea, as it would make the tank easier to detect. Furthermore, escaping gases were dangerous for the infantry that frequently rode on the tank. However, the People's Commissar of Tank Production, Malyshev, approved the IS with a 122 mm gun, since there was no other way to obtain a 122 mm gun quickly.

Initially, the D-25 had a screw breech, later replaced by a semi-automatic sliding breech. Various other changes were made: replacement of the muzzle brake, reinforcement of the recoil mechanism, increase of ammunition capacity to 30 rounds. After trials in 1943, it was decided that the 122 mm gun was powerful enough to destroy enemy tanks, artillery, and fortifications at large distances.

On November 21st, the D-25T with a new muzzle brake was tested against a Panther tank. The 122 mm blunt tipped shell could penetrate the 85 mm armour plate from 1200 meters. Considering that the tank burned, and was penetrated previously, this result was deemed inconclusive. Later, the new gun was tested on tanks in better condition, and a new shell was developed that could guarantee penetration at 1200-1300 meters.

The D-25T gun was powerful and effective. A downside was a low rate of fire due to an artillery type two-piece round, but the Red Army had no other alternative.

The IS, armed with a 122 mm gun, became the most powerful vehicle used by the Red Army. Breakthrough regiments used these tanks, immediately acquiring Guards status after formation. Due to the ability to penetrate any German tank at a large distance, German high command issued orders to avoid engaging these tanks.

The D-25T was also modified to be used on the ISU-122, under the index D-25S.

Note: the article's assertion that two-piece ammunition leads to a lower rate of fire is not necessarily correct. Yes, the single piece IS-85 could fire faster than the two-piece IS-122, but single piece 122 mm ammunition used in the T-44-122 did not result in an increased rate of fire.

In the summer of 1942, Soviet forces suffered a defeat at Kharkov. Taking advantage of the weakened defenses of the South and South-Western fronts, the Germans began a strategic push to the Volga and the Caucasus. In the beginning of August, the 6th army approached Stalingrad.

The battle for the city is known as one of the largest land battles in WWII. The Germans continued their advance until the fall, pushing the Red Army to the Volga. In September, battles were fought in Stalingrad itself, with previously unseen ferocity, not just for blocks or streets, but commonly, for floors, and even rooms.

After unsuccessful counterattacks in August-September, understanding its grim position, Soviet high command prepared for a strategic counteroffensive. Its goal was the encirclement and destruction of German forces at Stalingrad. The victory was necessary not only from a military point of view, but from a morale one: the people of the USSR were tired of retreating. A message needed to be sent that the Wehrmacht could be, and must be, defeated.

The counterattack was to be performed with the forces of three fronts: Don, South-Western, and Stalingrad. 14 armies were gathered for this operation, codenamed "Uranus".

On November 19th, 1942, early in the morning, three and a half thousand guns and mortars opened fire on German positions. The barrage lasted over an hour, followed by tanks and infantry. General Romanenko's 5th tank army penetrated the defenses of the 2nd Corps. Through the whole day, with bad visibility and in poor terrain, columns of Soviet vehicles plunged forward, deepening the breakthrough. On that day, the Red Army advanced 20 kilometers. The Germans could not stop the offensive.

By November 23rd, 1942, the ring around the 6th Army was closed. Fighting in Stalingrad would continue, but only three months remained until the surrender of the Germans at Stalingrad.

Rocket and Artillery Day is celebrated on November 19th, in honour of the artillery barrage that signaled the beginning of the Soviet offensive at Stalingrad.

Experimental prototype: 1 000 000 rublesThe costs include the "triplex" development from 1932

#27 project for arming the BT with a 107 mm gun. The project is not formalized."

The production figures are indicative of the early T-26 problems, but all the good stuff is in the experimental section. The heavy triplex SPG is, of course, the SU-7, but the BT with a 107 mm gun is something I have never heard of before.

Thursday, 21 November 2013

Some of you may have seen a pretty crazy tank model, designed by Soviet engineer Tsyganov.

You may also have read that it could achieve a great speed, over 100 kph! This was possible through the very complicated suspension system:

"February 10th, 1935 Top secret

Memo attached to the "BT" project designed by comrade Tsyganov, 4th tank regiment

This design of the BT tank proposed by the 4th tank regiment alters the method of the vehicle's movement, and has advantages over earlier designs, such as:

With the same speed of the chain (track) or, which is the same, the wheel, the tank has a speed that is twice as high as a regular tank with a caterpillar track.

Using a chain of wheels instead of a mechanical track, the tank does not knock its track links against the ground, and moves quietly.

In this design, the track moves half as fast as the vehicle. Due to this, the energy required to move at 100 kph is equal to the energy previously required to move at 50 kph on regular tracks.

The wheels are held by flexible tracks, which, for additional flexibility, are made of separate segments with ball and socket joints. The suspension is made with leaf springs, one immobile, and two for balance, which let individual track segments hug the ground. In order to make movement smoother, the tank's tracks are rubber on the outside, and steel on the inside.

This design does not require a more powerful motor, as the existing 400 hp motor is powerful enough. Subsequent reasoning is provided in the form of mathematical calculations. The calculations are made using data extracted from the works of professor Zaslavskiy, professor Chudakov, and other authors with materials relevant to the design of such vehicles."

I will leave out the math, as whoever will benefit from it probably doesn't need a translation to figure it out. I'll extract some useful figures, though:

Maximum chain wheel RPM: 422

Minimum chain wheel RPM: 58.5

Maximum chain speed: 14.5 m/s

Minimum chain speed: 2 m/s

Maximum tank speed: 104 kph

Minimum tank speed: 14.4 kph

Combat mass: 12 tons

Then, the design of the track chain and upper leaf spring is shown. Designs of other suspension elements are shown further in the memo, but this is all I have.

"Regimental commander Hong

Regimental commissar Zubenko

Calculations by engineer Bessonov

City of Kharkov"

Several of Tsyganov's projects were accepted and built, but not this one, due to its complexity.

Wednesday, 20 November 2013

Following up the 1941 plans, let's look at the plans for the next year. The past few months have been hard for the USSR. While the German plan to cripple the Red Army in one swift strike failed, industry suffered, and a number of projects were cut. Let's see what the changes look like:

CAMD RF 38-11355-694

6000 KV tanks are to be built, including 1200 in the first quarter (350 in January, and then 50 more each subsequent month). This is 6 times more than the total amount of KV tanks Kirov Factory was assigned during the peace time, but ChTZ is set to help. There is no radio-less version (all KV tanks had radios). One tank costs 635,000 rubles.

15,000 T-34s are to be produced, 6,000 with radios and 9,000 without. The orders are split among three factories: #183, #112, and STZ. A T-34 with a radio costs between 274,500 and 324,500 rubles. A T-34 without costs 269,000-320,000. Leaving out a radio did not result in significant savings, only 5,000 rubles per unit. The price difference between #183 and the other factories is explained by a redesign to the tank, to increase reliability and simplify manufacturing that did not have time to spread.

There is still a plan for factory #174 to produce T-50 tanks, 600 with a radio and 900 without. One T-50 costs 298,000 rubles, a radio on it is an extra 2,000. The cost is one of the reasons why the tank did not make it into production. Why make a light tank with a 45 mm gun when you can have a medium tank with a 76 mm gun for basically the same price?

Next we have T-60s. A total of 27,500 were to be built by a number of factories (#37, ZiS, HTZ, GAZ, Kolominskiy), only 4650 of them with radios. Unlike variably priced T-34s, each T-60 costs the same amount: 81,000 for a regular version, 82,700 for one with a radio. A third of the cost of a T-34? Now that's how you make a light tank!

The total numbers add up to 500,000 units, 8150 of which will be needed in the first quarter. The bill totals up to, 110,181,050,000 rubles for the tanks alone, not including service, parts, crew salaries, etc. War is expensive.

Tuesday, 19 November 2013

Submitting ridiculous projects wasn't only an officer's job, anyone could have a go. Red Armyman N. N. Nilov decided to do his engineering duty for the Motherland with his invention that he called "4-turreted tank".

CAMD RF 38-11355-1317

The tank was developed between August 21st 1941 and April 18th 1942. In this time, Nilov envisioned a tank that looked like a T-100, but with two extra turrets...on the sides. Much like the T-100 (or at least the proposed T-100Z), the top turret had a big gun (140 mm, with 84 shells) along with machine guns (one coaxial, one collapsible on the roof), and the smaller turret had a 45 mm gun. The side turrets only had high caliber machine guns. The tank carried 10 crewmen. The armour wasn't particularly impressive, only 60 mm in the front hull, rear, and on the turrets, and 45 mm on the sides. However, the tank was supposed to accelerate to 120 kph using a 1200 hp engine. At 80 tons, that would have been doubtful.

Despite the infeasible design, the tank has some useful features, such as a protected ammunition rack at the bottom of the hull and armour screens that cover the tracks.

An interesting thing about the design is the pointed shape of the side turrets. It doesn't have a function, the designer just chose to make his creation look like domes in his home city of Bukhara.

Monday, 18 November 2013

When the Red Army encountered Finnish defenses during the Winter War, they realized that they had no self propelled guns capable of defeating concrete fortifications. Using the chassis of the three new heavy tanks (SMK, T-100, and KV), new self propelled artillery projects were developed. The only one of them that really got anywhere was the KV-2. Various other projects, such as the 212 SPG (known to many more as Object 212) got somewhere before slowly dying due to a sudden lack of an enemy with fortifications they would be needed against.

CAMD RF 38-11355-101

"Act on the state of completion of the object #212 (SPG)

The current act is composed to state that the following work was performed on the experimental object #212 (SPG) as of May 29th, 1941.

Sketches and technical project, costing 100,000 rubles.

Working blueprints, costing 200,000 rubles.

Armoured hull produced at the Izhor factory, costing 150,000 rubles.

The total cost of the work was 450,000 rubles, which is the sum that must be paid in advance to the project. The final cost will be computed using report calculations.

Lantzberg, Kotin, Rogachev, Shpitanov"

However, the project stalled way before May. The SPG has been sitting in that condition since March. Soon after this document was written, the war started, and the 212 was shuffled around from factory to factory, eventually disappearing forever.

Work on a self propelled high caliber howitzer had to be put on hold, but the artillery officers never forgot about it. Eventually, the Artillery Committee ordered it back up and running. Item #12 on a list of projects at the Kirov factory (CAMD RF 38-11369-91) contains the following:

"203 mm self propelled B-4 howitzer on the chassis of a KV-1S tank. Kirov Factory and factory #172. Planned work for the Artillery Committee.

The Artillery Committee planning session from April 15th, 1942, identified the need for a self propelled Br-2 gun on the KV chassis. As a result of experience in the construction of self-propelled guns in 1942-1943, it was deemed possible to install a B-4 howitzer in a semi-enclosed SPG. The Kirov factory and factory #172
have a contract with Artkom's 16th department regarding this project. Each factory is developing the project separately."

The need for a Br-2 on a KV chassis appears even earlier, in a document from November of 1941 that lists SPG projects for 1942 (CAMD RF 81-12104-115).

In November of 1943, the GAU chief, Colonel Yakovlev, wrote a letter to the People's Commissar of Tank Manufacturing Malyshev:

"According to your announcement, the Commissariat of Tank Manufacturing intends to continue work on design and production of experimental self propelled 152 mm Br-2 and 203 mm B-4 guns, which was ordered by the GAU in 1940, but was interrupted in 1941 due to the start of the war.

The GAU considers this work to be necessary. The blueprints for the guns and ammunition have been sent to the Kirov Factory SKB-2 by GAU on June 19th of this year.

Orders to deliver a 152 mm Br-2 gun and 203 mm B-4 howitzer to factory #100 have been given.

The technical requirements, revised based on experience of the war, are currently being completed at GAU and will be sent to you in the coming days."

CAMD RF 81-12063-1

That desire was fulfilled in less than a year, in the form of the S-51 self-propelled howitzer. Unlike the previous designs, where the gun was fully enclosed, the S-51 mounted it on a mostly open platform, with a shield in the front that could flip up to protect the crew from shrapnel and bullets.

"An Order of the State Committee of Defense

On the question: manufacturing a party of 203 mm self propelled howitzers B4-S51

The Red Army accepts the 203 mm B4-S51 howitzer, developed by TsAKB NKV, consisting of the 203 mm B-4 field howitzer model 1931 on a KV-1S tank chassis.

NKTP (comrade Malyshev) and GURT of the Red Army (comrade Sosenkov) must deliver 50 repaired KV-1S tanks to NKV, without the rotating turret, and with an intact suspension, engine (with less than 10% of its lifetime hours expended), transmission, and spare parts by the following dates:

25 units by August 10th

25 units by August 25th

NKV (comrade Ustinov) must manufacture parts and organize mass production of 203 mm B4-S51 howitzers in the following time frame:

By August 20th: 20 self propelled howitzers

By August 30th: 30 self propelled howitzers

During mass production, remove the defects discovered during trials. TsAKB NKV (comrade Grabin) must edit the blueprints accordingly, and turn them in by August 1st to GAU of the Red Army."

CAMD RF 81-12038-413

CAMD RF 38-11369-287

"The 203 mm self propelled "S-51" howitzer built by the NKV TsAKB, consisting of a 203 mm model 1931 howitzer (B-4) on a turretless KV-1S tank with a foundation plate for the installation of the rotating part of the howitzer and slots cut in the roof of the hull for the recoil mechanisms underwent trials. The main technical-tactical characteristics of the self propelled S-51 howitzer are as follows:

Ballistics

Caliber: 203.2 mm

Muzzle velocity: 607 m/s

Maximum chamber pressure: 2366 kg/cm^2

Shell mass: 100 kg

Muzzle energy: 1900 ton-meters

Maximum range: 18025 meters

Combat

Vertical range: 0-60 degrees

Horizontal range: +/- 4 degrees

Ammunition capacity: 12 rounds

Rate of fire: 1-1.5 RPM

Full combat weight (according to TsAKB data): 49.7 tons

Crew: 10

Maximum speed: 30 kph

Design

Bore axis height: 2793 mm

Recoil length:

Long (up to 16 degrees 30 minutes): 1200-1300 mm

Short (from 16 degrees 30 minutes and up): 850-890 mm

Initial pressure in return gear: 40+/-2 atmospheres."

In the meantime, GAU Artkom was developing their own 203 mm SPG at Perm (factory #172). The vehicle, indexed M-22, was very similar to the S-51: a SU-152 with the casemate removed, and B-4 howitzer added.

CAMD RF 38-11369-108

Thankfully, sane artillery projects were also being developed at the time, such as a SU-76 with a 122 mm howitzer, to make a more portable and cheaper SU-122.

CAMD RF 38-11369-481

"May 1944

To the director of the Gorkiy Automotive Factory

I ask you to order the Construction Bureau to explore the possibility of installing a 122 mm howitzer in an SPG on the chassis of the SU-76. In order to obtain the tactical-technical characteristics of the 122 mm howitzer, contact the Construction Bureau of the NKV factory #9 in Sverdlovsk.

Report back on your decision and subsequent actions.

Chief of the GBTU KA

Lieutenant-General of the Tank Forces

Vershinin"

The exact date of the above document was cut off in the scan, but seeing as how all the other stamps and signatures on it are from June, it was likely late May.